Spread-spectrum clocking has emerged as a cost-effective technique for reducing the spectral density of electromagnetic interference (EMI) generated by synchronous communications systems. With a regular clock, the EMI is concentrated near the frequency of the clock. Spread-spectrum clocking varies the frequency or phase of the clock, thereby spreading the EMI over a broader spectrum. Spread-spectrum clocking is used in many areas, for example in serial communications having an embedded clock signal.
Acquiring and tracking such a clock signal can be difficult. Failure to track the clock signal results in unacceptably high bit error rates. One common remedy is to keep the spreading of the clock signal at the transmitter within a narrow range to facilitate clock recovery at the receiver. Of course, this limits the efficacy of the spreading in reducing EMI.